1. Field of the Invention
This invention relates generally to smoke detection and more particularly is directed towards a new and improved method and system for detecting the presence of an aerosol such as smoke using a small number of simple components arranged and operated in a highly efficient manner and with low power requirements.
2. Description of the Prior Art
Most optical smoke detectors now in use employ reflected light principles in which a light source is directed into an examination zone in which smoke is adapted to pass in the event of a fire. A photocell is also directed at the zone and is adapted to respond to light reflected from any smoke particles illuminated by the light source.
Reflected light smoke detectors of the sort described above typically function in either of two operating modes. In one mode, the light source is operated on a continuous basis which makes them impractical for battery powered units or for line powered units employing standby battery power. While detectors of this type are relatively simple to fabricate and can be highly sensitive, they are somewhat slow to react because of the response characteristics of the photo resistive cells generally used in this application.
The second mode of operation is one in which the light is pulsed in order to reduce current drain. While the pulsing type of smoke detector reduces current demand, photodetectors of much faster response are required with a concurrent increase in cost. Also, the light source employed in the pulse type unit must be capable of higher output than one of a steady state detector. Further costs are incurred by the necessity of including an amplifier to compensate for the reduced photo gain of the high speed detector used in this type of system.
Accordingly, it is an object of the present invention to provide improvements in smoke detectors, especially low current drain smoke detectors.
Another object of this invention is to provide a battery powered smoke detector of simple, low cost construction characterized by high sensitivity and quick response.
A further object of this invention is to provide a novel method and associated system for detecting smoke.